There is great interest in elucidating the corrosion mechanism of magnesium, and different experimental methods and techniques are explored with this purpose. Among the scanning probe techniques, scanning electrochemical microscopy (SECM) is delivering some promising results in recent years. In particular, the use of ion selective microelectrodes (ISME) as SECM sensing probes allow monitoring of the temporal and spatial distribution of different ionic species related to the corrosion reactions. However, a serious disturbance in the measured potential can be observed when it comes to galvanic coupling or polarization of the samples. This work explores the factors that affect the magnitude of the electrical field effects associated with the galvanic coupling, and describes an experimental arrangement for potentiometric SECM able to avoid the unwanted contribution of the potential field. The performance of a double barrel electrode assembly comprising an ion selective microelectrode and an internal reference electrode was compared to that of a conventional single barrel ISME in order to establish its applicability for the investigation of corrosion systems presenting electrical field distributions. (C) The Author(s) 2018. Published by ECS.